This invention relates to an improvement in fluidic handling servovalves, and, more particularly, to a ball-tpye motor for providing a fluidic mechanical feedback function in the valve.
Known fluidic servovalves are comprised of three basic elements--the pilot stage, the boost valve and a feedback mechanism. The pilot stage may be an electrically operated flapper type valve having an armature around which is wound an electrical coil and which moves between magnetic pole pieces to position a flapper. The flapper then cooperates with one or more nozzles for regulating a control fluid dependent upon the position of the flapper with respect to the nozzle or nozzles. In the alternative, the pilot stage valve may be comprised of a jet pipe for issuing a jet of fluid to one or more receiving ports. The receiving ports then supply a control fluid dependent upon the position of the jet pipe with respect to the receiving ports. The position of the jet pipe may also be controlled by an electrical operator. Also, electrically driven spool-type valves or fluid amplifiers have been used in the pilot stage.
The boost valve is most often a spool valve having a plurality of lands including lands at either end of the spool. The lands at the ends of the spool define control chambers within the bore in which this spool moves. These control chambers are connected to receive the control fluid. A further land controls the amount of fluid issuing from a supply port and received by at least one output port. The position of the spool is controlled by the control fluid supplied by the pilot stage and will determine the amount of output fluid received by the output port. The fluid received by the output port is then used to position an actuator, most usually in the form of a piston.
The feedback mechanisms for providing stable and proportional operation of the servovalves have taken several forms. For example, the actuator may control a variable capacitor, inductor or resistor for providing an electrical feedback to the circuit which provides the electrical input to the pilot stage valve. A mechanical linkage may be connected between the spool of the boost valve and the flapper or jet pipe of the pilot stage valve. Pure hydraulic feedbacks from the output of the spool valve back to control chambers for the boost valve have been devised. Also, combination mechanical and fluidic feedbacks have been devised. But so far no one has devised a simple and economical motor, such as the ball-type motor of this invention, which, in response to the output fluid from the boost valve, will reposition the movable element of the pilot stage valve.